The invention relates to a filter device for filtering compressed air comprising a principal fluid duct extending between an inlet and an outlet and divided by filter means, through which compressed air flows in operation, into an inlet flow section and an outlet flow section.
Filter devices of this type, as are disclosed for instance in the assignee""s xe2x80x9cPneumatic-Katalog 97/98xe2x80x9d, page 9.3/15-1 as a rule comprising a housing with a principal body having the inlet and the outlet and a vessel-like filter shell fixed thereto in a detachable manner. In the space defined between the principal body and the filter shell a replaceable and preferably cartridge-like filter means is sealed, which divides up the principal fluid duct extending between the inlet and the outlet into an outlet flow section associated with the inlet and an inlet flow section associated with the outlet. Compressed air supplied by way of the inlet is cleaned on flowing through the filter means and freed of impurities. Such a filter means is to an overwhelming extent employed for the treatment of compressed air in compressed air supply systems, it normally being utilized as part of so-called servicing units, which may include further components such as regulators or oilers.
In the case of excessive contamination of the filter means employed replacement is necessary for further operation of the machines and devices connected with the associated compressed air supply system without impairment. In this respect finding the right point in time for cleaning or replacement of the filter means is a problem. Although the assignee is aware of plans to find the point in time in question on the basis of the pressure drop between the inlet flow section and the outlet flow section of the principal fluid duct, this method of measurement is extremely inaccurate.
Object of the present invention is to provide a filter device of the type initially mentioned, in the case of which the point in time appropriate for replacement or cleaning of the filter means may be reliably found.
In order to achieve this object the filter device is provided with means for the recognition of the degree of contamination of the filter means, which comprise a pressure differential sensor means responsive to the pressure differential between the inlet flow section and the outlet flow section and furthermore a flow rate sensor means responsive to the rate of flow in the principal fluid duct and is further provided with an electronic evaluating means for linking the detected pressure differential data and the flow rate data to produce a condition value relevant for the degree of contamination of the filter means for comparison with predetermined threshold values.
The recognition means for the degree of contamination of the filter means used accordingly process both the pressure differential between the inlet flow section and the outlet flow section of the principal fluid duct as well as the instantaneous flow rate in the principal fluid duct, the detected values being linked in an electronic evaluating means to yield a condition value relevant for the degree of contamination, such condition value then being able to be compared with the predetermined threshold values. The comparison measures may in principle be undertaken externally, as for example by comparison with predetermined reference tables, but are however preferably performed in the electronic evaluating means as well, which for this purpose may be provided with a comparison means.
By taking into account both the pressure differential and also the flow rate it is possible for the degree of contamination to be found reflecting the current operating conditions, it being taken into account as well that the pressure differential varies in accordance with the given flow rate. If only the pressure differential were to be employed for recognition of the degree of contamination, this could admittedly be used in connection with permanently set flow rate to indicate certain features of the degree of contamination. However, once in the operation of a compressed air supply network changes occur in the flow rate owing to switching loads on or off, this results in faulty data if the same set value applies with only one pressure differential threshold value. By additionally taking into account the flow rate it is then possible to see, independently of the flow rate, that a critical degree of contamination has been reached.
Further advantageous developments of the invention are defined in the dependent claims.
The electronic evaluating means preferably comprises a memory for storage of threshold values applying at least one filter means type. If the filter device is only designed for use with one single specific filter means type, the threshold values may be assigned in accordance with this one type of filter means. As an alternative it is possible for a plurality of different filter means types to be stored in the memory means, a selection means being present, which in a manner dependent on the actually installed filter means type renders possible a type-specific threshold value selection. This can for example be ensured by having manual settings, more especially by using a switch arrangement and/or using a potentiometer arrangement. However, a design is more convenient in which the filter device additionally has a detection means, which has means for the recognition of the currently installed filter type and which can generate a filter type specific electrical detection signal, which may be employed in the evaluating means for the type specific selection of threshold values. The detection means may for example have activating means provided on the filter means, such activating means cooperating directly or indirectly with the sensor means on the housing when the filter means is installed for producing a detection signal.
The filter device renders possible even more universal operation, when the means for the recognition of the degree of contamination additionally comprise a sensor means responsive to the inlet pressure in the inlet flow section of the principal fluid duct, the inlet pressure value found being taken into account in the electronic evaluating means for finding the instantaneous condition value. In this case for finding the critical degree of contamination values the current pressure conditions are taken into account as well, it being possible for the arrangement to be such that in a memory means different threshold values are stored in a memory means for one or more types of filter means in each case dependent on the inlet pressure, such different threshold values being able to be selected using a selection means dependent on the inlet pressure.
It is an advantage if the threshold values for one respective filter means may be set in a variable manner so that if necessary it is possible to make adaptations or with respect to further types of filter means to select particular specific threshold values.
The filter device may furthermore comprise an indicator means, which indicates the current condition value of the degree of contamination and/or reaching or exceeding the threshold values for one filter means. The indication can for example be optical or acoustic and/or involve the issue of an electrical indicating signal, which may be processed if required. The threshold values for a respective filter means may more particularly be in the form of a threshold value characteristic curve or of a threshold value characteristic curve set.
If required it is additionally possible to have a predetermined threshold value in the form of a maximum pressure differential value independent of the flow rate, which for example corresponds to a condition, in which profitable operation is no longer possible.
The evaluating means could be provided externally of the filter device. However, to have compact dimensions it is preferred to use a design of the evaluating means as a direct component of the filter device or of a compressed air servicing device comprising the filter device in it. In any case the evaluating means may be integrated in a control means, which controls certain machine or device operation sequences.